Conventionally, there has been a fluid device including a compression mechanism and an expansion mechanism as disclosed in Japanese Laid Open Patent Publication No. 2003-138901. The fluid device has a rotary compressor accommodated in the lower part of the casing and a scrollable expander accommodated in the upper part of the casing. The fluid device also includes an electric motor between the compressor and the expander. The compressor and expander are coupled to both ends of a drive shaft which is connected to the motor.
The compressor compresses a refrigerant. The compressed refrigerant discharges heat in a heat exchanger and is then expanded by the expander. The expanded refrigerant absorbs heat in another heat exchanger and returns to the compressor. This cycle is repeated. In the expander, rotational power generated by the expansion of the refrigerant is recovered. The recovered rotational power and the rotational power of the electric motor drive the compressor. As a result, efficient driving is realized.